Method for recovering co2

Abstract

To provide a method for recovering CO2, with a high CO2 yield and at a low recovery cost.SOLUTION: A method for recovering CO2 includes a plurality of steps including a CO2 adsorption step of introducing a target gas into one or more adsorption towers 2, 12 filled with an adsorbent and adsorbing CO2, and a CO2 recovery step of desorbing and recovering CO2 adsorbed on the adsorbent. The CO2 recovery step includes a negative-pressure water vapor CO2 recovery step of recovering CO2 while reducing pressure to atmospheric pressure or less while circulating water vapor in the adsorption tower, and a negative-pressure CO2 recovery step of recovering CO2 while reducing the pressure in the adsorption tower to the atmospheric pressure or less. The CO2 adsorption step and the CO2 recovery step are repeatedly performed. In the CO2 recovery step, the negative-pressure CO2 recovery step is performed after the negative-pressure water vapor CO2 recovery step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for capturing CO2, and more particularly to a method for capturing CO2 by separating and capturing CO2 in a target gas using an adsorbent. [Background technology]

[0002] From the perspective of reducing greenhouse gas emissions, there is a need to build systems that can capture CO2 from various emission sources such as thermal power plants, steel mills, cement plants, and boilers, and CO2 capture technologies such as chemical absorption, PSA (Pressure Swing Adsorption), TSA (Temperature Swing Adsorption), and membrane separation are being developed. In PSA, the target gas is introduced into an adsorption tower filled with adsorbent, and CO2 is adsorbed at atmospheric pressure or under pressure. The adsorbed CO2 is then desorbed and captured by depressurizing the adsorption tower.

[0003] To further reduce CO2 emissions, it is desirable to capture CO2 with a high CO2 yield. Reducing the pressure in the adsorption tower to a low level increases the amount of CO2 desorbed and achieves a high CO2 yield, but this increases the cost of capture.

[0004] By reducing the pressure in the adsorption tower while introducing a gas with a low CO2 concentration (rinse gas), CO2 desorption can be promoted, reducing the energy required for CO2 capture and improving the CO2 yield. In particular, water vapor is often used for desorption in CO2 capture devices because it is easy to separate from the captured gas and it is easy to obtain high-purity CO2 (see, for example, Patent Document 1). It is also known that, depending on the type of adsorbent, adsorbing water vapor can have a favorable effect, such as reducing the energy required for CO2 desorption (see, for example, Patent Document 2).

[0005] Furthermore, depressurizing the adsorption tower while introducing steam promotes CO2 desorption, improving the regeneration of the adsorbent, reducing the amount of CO2 lost in the early stages of the adsorption process and improving CO2 yield. Furthermore, compared to depressurization alone, introducing steam increases the amount of CO2 adsorbed per amount of adsorbent, allowing for the downsizing of the equipment. Furthermore, compared to depressurization alone, CO2 can be desorbed at higher pressures, making it possible to reduce the energy required for CO2 capture (i.e., the power required for the vacuum pump). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6302309 [Patent Document 2] Patent No. 6721020 Summary of the Invention [Problem to be solved by the invention]

[0007] However, with many adsorbents, when excessive water vapor is adsorbed, CO2 breaks through quickly, resulting in a decrease in the amount of CO2 adsorbed, which can increase the cost of CO2 capture.

[0008] Therefore, an object of the present invention is to provide a method for recovering CO2 with a high CO2 yield and low recovery costs. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, a first CO2 capture method of the present invention is a CO2 capture method in which a target gas, which is a mixed gas consisting of two or more gas components including CO2, is introduced into one or more adsorption towers filled with an adsorbent, and CO2 is separated and captured from the target gas. The method comprises multiple processes including a CO2 adsorption process in which CO2 in the target gas is adsorbed by the adsorbent, and a CO2 capture process in which the CO2 adsorbed by the adsorbent is desorbed and captured. The CO2 capture process includes a negative-pressure steam CO2 capture process in which water vapor is circulated through the adsorption tower and the pressure in the adsorption tower is reduced to below atmospheric pressure, thereby desorbing the CO2 adsorbed by the adsorbent and capturing it as a captured gas, and a negative-pressure CO2 capture process in which the pressure in the adsorption tower is reduced to below atmospheric pressure, thereby desorbing the CO2 adsorbed by the adsorbent and capturing it as a captured gas. The CO2 adsorption process and the CO2 capture process are repeated, and the CO2 capture process is characterized in that the negative-pressure steam CO2 capture process is performed after the negative-pressure steam CO2 capture process.

[0010] Furthermore, in order to achieve the above-mentioned object, the second CO2 recovery method of the present invention is a CO2 recovery method in which a target gas, which is a mixed gas consisting of two or more gas components including CO2, is introduced into one or more adsorption towers filled with an adsorbent, and CO2 in the target gas is separated and recovered, and the method comprises a plurality of steps including a CO2 adsorption step in which CO2 in the target gas is adsorbed by the adsorbent, and a CO2 recovery step in which the CO2 adsorbed by the adsorbent is desorbed and recovered, and the CO2 recovery step includes the steps of: circulating water vapor through the adsorption towers; and reducing the pressure in the adsorption towers to atmospheric pressure or below, The system includes a negative pressure steam CO2 recovery process in which the CO2 adsorbed on the adsorbent is desorbed and recovered as a recovered gas, and a negative pressure CO2 recovery process in which the CO2 adsorbed on the adsorbent is desorbed and recovered as a recovered gas while reducing the pressure in the adsorption tower to below atmospheric pressure.The system includes a first cycle in which the CO2 adsorption process and the negative pressure steam CO2 recovery process are repeatedly performed, and a second cycle in which the CO2 adsorption process and the negative pressure CO2 recovery process are repeatedly performed, and is characterized in that after the first cycle is performed at least once, the second cycle is performed at least once.

[0011] Furthermore, in order to achieve the above-mentioned object, a third CO2 capture method of the present invention is a CO2 capture method for separating and capturing CO2 in a target gas, which is a mixed gas consisting of two or more gas components including CO2, introduced into one or more adsorption towers filled with an adsorbent, and the method comprises a plurality of steps including a CO2 adsorption step for adsorbing CO2 in the target gas onto the adsorbent, and a CO2 capture step for desorbing and capturing the CO2 adsorbed onto the adsorbent, wherein the CO2 capture step includes circulating water vapor through the adsorption tower and desorbing the CO2 adsorbed onto the adsorbent while reducing the pressure inside the adsorption tower to below atmospheric pressure. and a negative pressure CO2 capture process in which the CO2 adsorbed by the adsorbent is desorbed while reducing the pressure in the adsorption tower to below atmospheric pressure and the CO2 is captured as a captured gas. The system has a first cycle in which the CO2 adsorption process and the negative pressure steam CO2 capture process are repeatedly performed, and a second cycle in which the CO2 adsorption process and the CO2 capture process in which the negative pressure steam CO2 capture process is performed after the negative pressure steam CO2 capture process are repeatedly performed, and is characterized in that the first cycle is performed at least once, and then the second cycle is performed at least once.

[0012] Furthermore, in the negative pressure CO2 capture process, a rinse gas may be introduced into the adsorption tower. Also, when there are three or more adsorption towers and at least one adsorption tower is performing the CO2 adsorption process, at least one of the other adsorption towers is performing the CO2 capture process, and at least one is performing a purge process in which a portion of the capture gas is introduced as a purge gas. [Effects of the Invention]

[0013] According to the CO2 capture method of the present invention, CO2 can be captured by repeatedly performing an operation that combines a negative pressure steam CO2 capture process and a negative pressure CO2 capture process so that the adsorbent can maintain a moderate level of moisture, thereby improving the CO2 yield and reducing the cost of CO2 capture. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an example of a CO2 recovery device to which the CO2 recovery methods of the first to third embodiments of the present invention can be applied. [Figure 2] FIG. 10 is a diagram showing an example of a CO2 recovery device to which the CO2 recovery methods of the fourth and fifth embodiments of the present invention can be applied. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing an example of a CO2 recovery apparatus to which the CO2 recovery methods of the first to third embodiments of the present invention, which will be described later, can be applied. As shown in Fig. 1, the CO2 recovery apparatus 10 includes an adsorption tower 2 filled with a CO2 adsorbent, a target gas supply line L1 that supplies a gas to be treated (raw material gas) to the lower part of the adsorption tower 2, an off-gas discharge line L2 through which CO2 in the gas to be treated is adsorbed in the adsorption tower 2 and discharged as off-gas, a recovery line L3 that is suctioned by a vacuum pump 3 and recovers CO2 from the lower part of the adsorption tower 2, a steam introduction line L4 that introduces steam to the upper part of the adsorption tower 2, and a rinse gas introduction line L5 that introduces a rinse gas to the upper part of the adsorption tower 2.

[0016] Each of the lines L1 to L5 is provided with an on-off valve V1 to V5. The target gas is a mixed gas consisting of two or more gas components including CO2, and preferably a gas containing CO2 with a main air component such as oxygen or nitrogen. For example, it is exhaust gas containing approximately 1 to 20% CO2 from various emission sources such as thermal power plants, steel mills, and cement factories. The pressure of the target gas is atmospheric pressure or higher, and is preferably 100 kPa(g) or lower in order to reduce the power required for pressure increase. The target gas supply line L1 may be provided with a blower for increasing the pressure of the target gas as necessary.

[0017] The adsorbent packed in the adsorption tower 2 is capable of repeatedly adsorbing CO2 in a gas containing moisture equal to or less than the saturated water vapor amount. Examples include activated carbon (including activated carbon molecular sieve), activated alumina, silica alumina, silica gel, zeolite, and amine carriers (amine compounds supported on porous carriers such as silica and silica gel). Activated carbon is preferred. Typical amine compounds supported on amine carriers include monoethanolamine, dimethanolamine, triethanolamine, tetraethylenepentamine, polyethyleneimine, methyldiethanolamine, isopropanolamine, diisopropanolamine, and dibutylamine.

[0018] Examples of the rinse gas include water vapor with a relative humidity of less than 100%, preferably 50% or less, air, oxygen, etc. Nitrogen, argon, helium, and other inert gases are also acceptable. There are no particular limitations on the temperature of the rinse gas, but it is preferably 25°C or higher and lower than 100°C.

[0019] The CO2 recovery methods shown in the first to third embodiments of the present invention include the following CO2 adsorption and recovery steps using the CO2 recovery device 10 configured as described above.

[0020] [CO2 adsorption process] The on-off valves V1 and V2 are opened, and the target gas is introduced into the adsorption tower 2 via the target gas supply line L1. The CO2 in the target gas is adsorbed by the adsorbent in the adsorption tower 2, and the remaining components are discharged as off-gas through the off-gas discharge line L2. After a predetermined time has elapsed, the on-off valves V1 and V2 are closed. In the present invention, this process is referred to as the CO2 adsorption process. Note that the CO2 concentration in the off-gas in the off-gas discharge line L2 may be monitored, and the operation may proceed to the next process when the CO2 concentration exceeds a predetermined value even before the predetermined time has elapsed.

[0021] [CO2 capture process] In the present invention, the CO2 recovery process, in which the CO2 adsorbed to the adsorbent in the above-mentioned CO2 adsorption process is desorbed from the adsorbent by sucking it out (so-called vacuuming) with a vacuum pump 3, includes the following two processes.

[0022] [Negative pressure steam CO2 recovery process] With the on-off valves V3 and V4 open, the pressure inside the adsorption tower 2 is reduced to below atmospheric pressure using the vacuum pump 3. Steam is then introduced through the steam inlet line L4 to desorb the CO2 adsorbed on the adsorbent and regenerate the adsorbent. Introducing steam, a gas with a low CO2 concentration, promotes CO2 desorption, and adsorbing the steam onto the adsorbent reduces the energy required for CO2 desorption. In the present invention, this process is referred to as the negative-pressure steam CO2 capture process. After a predetermined time has elapsed, the on-off valves V3 and V4 are closed. However, if the process proceeds directly to the negative-pressure CO2 capture process described below, only the on-off valve V4 is closed.

[0023] [Negative pressure CO2 capture process] With the on-off valve V3 open, the pressure inside the adsorption tower 2 is reduced to below atmospheric pressure using the vacuum pump 3, while the CO2 adsorbed on the adsorbent is desorbed. Furthermore, when this process is performed after the negative pressure steam CO2 capture process, the moisture adsorbed on the adsorbent is desorbed, regenerating the adsorbent, and moisture adhering to the adsorbent and the inner wall of the adsorption tower 2 also evaporates. This allows the surface of the adsorbent to be appropriately dried, while simultaneously lowering the temperature of the adsorbent, thereby increasing the amount of CO2 adsorbed in the subsequent CO2 adsorption process. In the present invention, this process is referred to as the negative pressure CO2 capture process.

[0024] In addition, during the negative pressure CO2 capture process, the on-off valve V5 may be opened to allow a rinse gas to flow through the rinse gas introduction line L5 to further dry the adsorbent. In this case, the on-off valves V3 and V5 are closed after the adsorbent drying is complete. If the introduction of the rinse gas makes the CO2 concentration of the captured gas unacceptable, the gas may be discharged to the outside of the system through the capture line L3 without being captured.

[0025] [First form example] The CO2 capture method according to the first embodiment of the present invention repeats a CO2 adsorption process and a CO2 capture process, and in each CO2 capture process, a negative pressure steam CO2 capture process is performed after the negative pressure CO2 capture process. This method allows CO2 to be captured while maintaining an appropriate moisture content in the adsorbent.

[0026] From the viewpoint of the power cost during suction by the vacuum pump 3, it is preferable that the implementation time of the negative pressure steam CO2 capture step in the CO2 capture step is shorter than the implementation time of the negative pressure CO2 capture step.

[0027] In the negative pressure steam CO2 capture process, the energy required for CO2 desorption can be reduced by bringing steam into contact with the adsorbent, but the amount of steam flowing from the steam inlet line L4 for CO2 desorption is smaller than that of the target gas, making it easier to control. Furthermore, while the flow rate and moisture content of target gases can fluctuate depending on the conditions of the emission source, there is no such effect when introducing steam from the steam inlet line L4.

[0028] Furthermore, by combining the negative pressure steam CO2 capture process with the negative pressure CO2 capture process, the amount of water used can be reduced compared to constantly introducing water into the steam in the CO2 capture process, reducing the cost of water steam. Also, the frequency of opening and closing the on-off valve V3 is reduced, which extends the life of the valve.

[0029] Furthermore, by implementing the negative pressure CO2 capture process, water is desorbed from the adsorbent and the moisture in the adsorption tower is evaporated, lowering the temperature of the adsorbent layer and increasing the amount of CO2 adsorbed per amount of adsorbent, making it possible to reduce the size of the entire capture device and improving the CO2 yield.

[0030] In the negative pressure steam CO2 capture process, the amount of moisture adsorbed by the adsorbent can be controlled by managing the temperature, steam introduction time, steam temperature, exhaust speed of the vacuum pump 3, and ultimate vacuum pressure. In the negative pressure CO2 capture process, the amount of moisture desorbed can be controlled by managing the temperature, suction time of the vacuum pump 3, exhaust speed, and ultimate vacuum pressure. The optimal amount of moisture to be adsorbed and desorbed by the adsorbent varies depending on the type and amount of adsorbent, the amount of CO2 in the target gas, etc.

[0031] [Second form example] The CO2 capture method according to the second embodiment of the present invention, like the first embodiment, repeatedly performs a CO2 adsorption step and a CO2 capture step, but differs as follows: First, a cycle in which only a negative pressure steam CO2 capture step is performed as a CO2 capture step after the CO2 adsorption step is called the first cycle. Also, a cycle in which only a negative pressure CO2 capture step is performed as a CO2 capture step after the CO2 adsorption step is called the second cycle.

[0032] The first cycle and the second cycle are repeated so that the first cycle is performed at least once and then the second cycle is performed at least once. This method allows CO2 to be captured while maintaining a state in which the adsorbent retains an appropriate amount of moisture, and similar to the first embodiment, it is possible to improve the CO2 yield and reduce the cost of CO2 capture.

[0033] [Third form example] The CO2 capture method according to the third embodiment of the present invention, like the first and second embodiments, repeatedly performs a CO2 adsorption step and a CO2 capture step, but differs as follows: First, a cycle in which only a negative pressure steam CO2 capture step is performed as a CO2 capture step after the CO2 adsorption step is defined as the first cycle. Also, a cycle in which a negative pressure steam CO2 capture step is performed as a CO2 capture step after the CO2 adsorption step is defined as the second cycle.

[0034] After the first cycle is performed at least once, the second cycle is performed at least once, and the first and second cycles are repeated. This method also makes it possible to improve the CO2 yield and reduce the cost of CO2 capture, similar to the first and second embodiments.

[0035] Figure 2 is a diagram showing an example of a CO2 recovery apparatus to which the CO2 recovery methods of the fourth and fifth embodiments of the present invention, which will be described later, can be applied. Unlike the CO2 recovery apparatus 10 shown in Figure 1, the CO2 recovery apparatus 20 shown in Figure 2 has three adsorption towers 12 and is a three-tower PSA (pressure swing adsorption) system. By using two or more adsorption towers, it is possible to continuously adsorb CO2 in the target gas and desorb and recover the CO2 adsorbed on the adsorbent.

[0036] As shown in Figure 2, the CO2 capture system 20 includes three adsorption towers 12 (adsorption towers 12a, 12b, and 12c) filled with a CO2 adsorbent. The system receives a supply of target gas (raw material gas) from a target gas supply source, adsorbs CO2 in the target gas within the adsorption towers 12, and discharges the adsorption towers 12 as off-gas. The CO2 is then sucked up by a vacuum pump 13 and captured from the bottom of the adsorption towers 12. Steam is introduced from the top of the adsorption towers 12. The captured CO2-rich gas, which has a high CO2 concentration, is temporarily stored in a CO2 capture tank 14, and a portion of the gas is introduced as purge gas from the bottom of the adsorption towers 12 and discharged as purge off-gas from the top.

[0037] The specific piping configuration of the CO2 recovery system 20 is as follows: Each adsorption tower 12 (12a, 12b, 12c) is provided with a lower pipe L17 (L17a, L17b, L17c) at its lower end and an upper pipe L18 (L18a, L18b, L18c) at its upper end.

[0038] A target gas supply line L21 connected to a supply source of gas to be treated is provided with a blower 11 that pressurizes the gas to be treated, and extends branched into target gas supply branch lines L21a, L21b, and L21c downstream of the blower 11. The target gas supply branch line L21a is connected to the lower pipe L17a of the adsorption tower 12a, the target gas supply branch line L21b is connected to the lower pipe L17b of the adsorption tower 12b, and the target gas supply branch line L21c is connected to the lower pipe L17c of the adsorption tower 12c.

[0039] Off-gas discharge branch lines L22a, L22b, and L22c extend from the off-gas discharge line L22, and the off-gas discharge branch line L22a is connected to the upper pipe L18a of the adsorption tower 12a, the off-gas discharge branch line L22b is connected to the upper pipe L18b of the adsorption tower 12b, and the off-gas discharge branch line L22c is connected to the upper pipe L18c of the adsorption tower 12c.

[0040] Branch recovery lines L23a, L23b, and L23c extend from the recovery line L23. The branch recovery line L23a is connected to the lower pipe L17a of the adsorption tower 12a, the branch recovery line L23b is connected to the lower pipe L17b of the adsorption tower 12b, and the branch recovery line L23c is connected to the lower pipe L17c of the adsorption tower 12c. A vacuum pump 13 is attached to the recovery line L23, which can suction the interior of each adsorption tower 12 (12a, 12b, 12c). The suctioned gas is recovered and stored in a CO2 recovery tank 14 as a CO2-rich gas with a high CO2 concentration.

[0041] Water vapor inlet branch lines L24a, L24b, and L24c extend from the water vapor inlet line L24. The water vapor inlet branch line L24a is connected to the upper pipe 18a of the adsorption tower 12a, the water vapor inlet branch line L24b is connected to the upper pipe 18b of the adsorption tower 12b, and the water vapor inlet branch line L24c is connected to the upper pipe 18c of the adsorption tower 12c.

[0042] The purge gas introduction line L25 connected to the CO2 capture tank 14 is provided with a gas pump 15, and extends branched into purge gas introduction branch lines L25a, L25b, and L25c downstream of the gas pump 15. The purge gas introduction branch line L25a is connected to the lower pipe L17a of the adsorption tower 12a, the purge gas introduction branch line L25b is connected to the lower pipe L17b of the adsorption tower 12b, and the purge gas introduction branch line L25c is connected to the lower pipe L17c of the adsorption tower 12c.

[0043] Purge-offgas discharge branch lines L26a, L26b, and L26c extend from the purge-offgas discharge line L26. The purge-offgas discharge branch line L26a is connected to the upper pipe 18a of the adsorption tower 12a, the purge-offgas discharge branch line L26b is connected to the upper pipe 18b of the adsorption tower 12b, and the purge-offgas discharge branch line L26c is connected to the upper pipe 18c of the adsorption tower 12c.

[0044] Furthermore, the target gas supply branch lines L21a, L21b, and L21c are respectively equipped with on-off valves Va1, Vb1, and Vc1. The off-gas discharge branch lines L22a, L22b, and L22c are respectively equipped with on-off valves Va2, Vb2, and Vc2. The recovery branch lines L23a, L23b, and L23c are respectively equipped with on-off valves Va3, Vb3, and Vc3.

[0045] The water vapor inlet branch lines L24a, L24b, and L24c are respectively equipped with on-off valves Va4, Vb4, and Vc4. The purge gas inlet branch lines L25a, L25b, and L25c are respectively equipped with on-off valves Va5, Vb5, and Vc5. The purge off-gas exhaust branch lines L26a, L26b, and L26c are respectively equipped with on-off valves Va6, Vb6, and Vc6.

[0046] The CO2 recovery methods shown in the fourth to fifth embodiments of the present invention use a CO2 recovery device 20 configured as described above, and are configured to repeat the following CO2 adsorption process, CO2 recovery process (negative pressure steam CO2 recovery process, negative pressure CO2 recovery process), and purge process in a predetermined order and at predetermined time intervals in each of the adsorption towers 12a, 12b, and 12c.

[0047] [CO2 adsorption process] In the CO2 adsorption step, the on-off valve Va1 (or Vb1 or Vc1) and the on-off valve Va2 (or Vb2 or Vc2) are opened, and the target gas is introduced into the adsorption tower 12a (or 12b or 12c) from the bottom via the target gas supply branch line L21a (or L21b or L21c). CO2 in the target gas is adsorbed by the adsorbent, and the remaining components are discharged as off-gas from the off-gas discharge branch line L22a (or L22b or L22c).

[0048] [Negative pressure steam CO2 recovery process] In the negative pressure steam CO2 capture process of the CO2 capture process, the on-off valves Va3 (or Vb3, Vc3) and Va4 (or Vb4, Vc4) are opened, and the pressure inside the adsorption tower 12a (or 12b, 12c) is reduced to below atmospheric pressure using the vacuum pump 13, while steam is circulated from the steam inlet branch line L24a (or L24b, L24c), thereby desorbing the CO2 adsorbed in the adsorbent and regenerating the adsorbent.The desorbed CO2 is then recovered and stored in the CO2 capture tank 14 as captured gas (CO2-rich gas with a high CO2 concentration) via the recovery branch line L23a (or L23b, L23c).

[0049] [Negative pressure CO2 recovery process] In the negative pressure CO2 capture step of the CO2 capture process, the on-off valve Va3 (or Vb3, Vc3) is open, but Va4 (or Vb4, Vc4) is closed, and the pressure in the adsorption tower 12a (or 12b, 12c) is reduced to below atmospheric pressure by the vacuum pump 13, while the CO2 adsorbed in the adsorbent is desorbed and the adsorbent is regenerated. The desorbed CO2 is recovered and stored in the CO2 capture tank 14 as a captured gas (CO2-rich gas with a high CO2 concentration) via the recovery branch line L23a (or L23b, L23c).

[0050] [Purge process] In the purge step, the on-off valves Va5 (or Vb5, Vc5) and Va6 (or Vb6, Vc6) are opened, and a portion of the captured gas stored in the CO2 capture tank 14 is introduced into the adsorption tower 12a (or 12b, 12c) from the bottom side via the purge gas inlet branch line L25a (or L25b, L25c). The air components (residual components) adsorbed to the adsorbent and the CO2 remaining in the adsorption column are discharged as purge off-gas from the purge off-gas outlet branch line L26a (or L26b, L26c).

[0051] [Fourth form example] In the CO2 recovery method according to the fourth embodiment of the present invention, the adsorption towers 12a, 12b, and 12c each repeat one cycle of "CO2 adsorption process, purging process, CO2 recovery process" → "purging process, CO2 recovery process, CO2 adsorption process" → "CO2 recovery process, CO2 adsorption process, purging process" to transition between processes. In each CO2 recovery process, a negative pressure CO2 recovery process is performed after a negative pressure steam CO2 recovery process (see Table 1).

[0052] [Table 1]

[0053] From the viewpoint of the power cost during suction by the vacuum pump 13, it is preferable that the implementation time of the negative pressure steam CO2 capture step in the CO2 capture step is shorter than the implementation time of the negative pressure CO2 capture step.

[0054] This method allows for continuous CO2 capture while maintaining the adsorbent's moisture content. Furthermore, by implementing a purging process, it is possible to capture CO2 at a higher concentration.

[0055] [Fifth form example] The CO2 recovery method according to the fifth embodiment of the present invention is similar to the fourth embodiment in that the adsorption towers 12a, 12b, and 12c each repeat a cycle of "CO2 adsorption step, purging step, CO2 recovery step" → "purging step, CO2 recovery step, CO2 adsorption step" → "CO2 recovery step, CO2 adsorption step, purging step" to transition from one step to another. In the fifth embodiment, a cycle in which only the negative pressure steam CO2 recovery step is performed as the CO2 recovery step in the cycle of the cycle is referred to as the first cycle (see Table 2). Also, a cycle in which only the negative pressure CO2 recovery step is performed as the CO2 recovery step is referred to as the second cycle (see Table 3).

[0056] [Table 2]

[0057] [Table 3]

[0058] In the fifth embodiment, the first and second cycles are alternately performed, and even with this method, it is possible to continuously capture CO2 at a higher concentration while maintaining the adsorbent in a state where it retains an appropriate amount of moisture, just like in the fourth embodiment.

[0059] In addition, in the fifth embodiment, the first cycle and the second cycle are alternately performed, but the first cycle and the second cycle may be repeated so that the first cycle is performed at least once and then the second cycle is performed at least once.

[0060] As a modified example, the negative pressure steam CO2 recovery step may be performed every few cycles, for example, the second cycle may be performed twice and the first cycle once, and this may be repeated as one combination.

[0061] As another modification, the first cycle may be performed ten times, and then the second cycle and the first cycle may be performed alternately. The effects of the present invention can be fully achieved even if the ratio of the negative pressure steam CO2 capture process and the negative pressure CO2 capture process is changed during operation.

[0062] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention. For example, the number of adsorption towers is not necessarily limited to one or three, and the present invention can be applied to any number of adsorption towers, including two, four, or more. [Explanation of symbols]

[0063] 2...adsorption tower, 3...vacuum pump, 10...CO2 recovery device, 11...blower, 12 (12a, 12b, 12c)...adsorption tower, 13...vacuum pump, 14...CO2 recovery tank, 15...gas pump, 20...CO2 recovery device, V1 to V5...opening and closing valves, Va1, Vb1, Vc1, Va2, Vb2, Vc2, Va3, Vb3, Vc3, Va4, Vb4, Vc4, Va5, Vb5, Vc5, Va6, Vb6, Vc6...opening and closing valves, L1...target gas supply line, L2...off-gas discharge line, L3...recovery line, L4...steam introduction line, L5...rinse gas introduction line, L17 (L17a, L17b, L17c)...lower piping , L18 (L18a, L18b, L18c)...upper piping, L21...target gas supply line, L21a, L21b, L21c...target gas supply branch line, L22...off-gas discharge line, L22a, L22b, L22c...off-gas discharge branch line, L23...recovery line, L23a, L23b, L23c...recovery branch line, L24...water vapor introduction line, L24a, L24b, L24c...water vapor introduction branch line, L25...purge gas introduction line, L25a, L25b, L25c...purge gas introduction branch line, L26...purge off-gas discharge line, L26a, L26b, L26c...purge off-gas discharge branch line

Claims

1. In one or more adsorption towers filled with adsorbent, ２ A target gas is introduced, which is a mixed gas consisting of two or more gas components including CO ２ CO separation and recovery ２ A method for recovering The adsorbent is used to adsorb CO ２ CO ２ an adsorption step; CO adsorbed on the adsorbent ２ CO is desorbed and recovered ２ It consists of multiple processes including a recovery process, The CO ２ In the recovery process, While circulating water vapor through the adsorption tower and reducing the pressure inside the adsorption tower to below atmospheric pressure, the CO adsorbed by the adsorbent is ２ and recover the CO2 as a recovered gas. ２ The recovery process, While reducing the pressure in the adsorption tower to below atmospheric pressure, the CO adsorbed by the adsorbent is ２ and recover it as a recovered gas. ２ The recovery process, There are The CO ２ Adsorption process and the CO ２ Repeat the recovery process, The CO ２ The recovery step is performed by ２ After the recovery step, the negative pressure CO ２ CO recovery process ２ How to collect.

2. In one or more adsorption towers filled with adsorbent, ２ A target gas is introduced, which is a mixed gas consisting of two or more gas components including CO ２ CO separation and recovery ２ A method for recovering The adsorbent is used to adsorb CO ２ CO ２ an adsorption step; CO adsorbed on the adsorbent ２ CO is desorbed and recovered ２ It consists of multiple processes including a recovery process, The CO ２ In the recovery process, While circulating water vapor through the adsorption tower and reducing the pressure inside the adsorption tower to below atmospheric pressure, the CO adsorbed by the adsorbent is ２ and recover the CO2 as a recovered gas. ２ The recovery process, While reducing the pressure in the adsorption tower to below atmospheric pressure, the CO adsorbed by the adsorbent is ２ and recover it as a recovered gas. ２ The recovery process, There are The CO ２ Adsorption process and the negative pressure steam CO ２ a first cycle in which the recovery step is repeatedly performed; The CO ２ Adsorption process and negative pressure CO ２ a second cycle in which the recovery step is repeatedly performed; and and A CO2 reactor characterized in that the first cycle is carried out at least once, and then the second cycle is carried out at least once. ２ How to collect.

3. In one or more adsorption towers filled with adsorbent, ２ A target gas is introduced, which is a mixed gas consisting of two or more gas components including CO ２ CO separation and recovery ２ A method for recovering The adsorbent is used to adsorb CO ２ CO ２ an adsorption step; CO adsorbed on the adsorbent ２ CO is desorbed and recovered ２ It consists of multiple processes including a recovery process, The CO ２ In the recovery process, While circulating water vapor through the adsorption tower and reducing the pressure inside the adsorption tower to below atmospheric pressure, the CO adsorbed by the adsorbent is ２ and recover the CO2 as a recovered gas. ２ The recovery process, While reducing the pressure in the adsorption tower to below atmospheric pressure, the CO adsorbed by the adsorbent is ２ and recover it as a recovered gas. ２ The recovery process, There are The CO ２ Adsorption process and the negative pressure steam CO ２ a first cycle in which the recovery step is repeatedly performed; The CO ２ Adsorption step, and the negative pressure steam CO ２ After the recovery process, the negative pressure CO ２ The CO ２ a second cycle in which the recovery step is repeatedly performed; and and A CO2 reactor characterized in that the first cycle is carried out at least once, and then the second cycle is carried out at least once. ２ How to collect.

4. Negative pressure CO ２ 4. The CO 2 recovery method according to claim 1, wherein a rinse gas is introduced into the adsorption tower in the recovery step. ２ How to collect.

5. There are three or more adsorption towers, and at least one of the adsorption towers is ２ When the adsorption step is being performed, at least one of the other adsorption towers is ２ 4. The CO purging method according to claim 1, wherein a recovery step is performed and at least one of the recovery gases is also performed, in which a part of the recovery gas is introduced as a purge gas. ２ How to collect.

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